1. Field of the Invention
The present invention relates to a side-valve type internal combustion engine, and particularly, to an improvement in a side-valve type internal combustion engine including valve seats disposed in an upper surface of a cylinder block having a cylinder bore and located in intake and exhaust ports which are juxtaposed in a circumferential direction of a cylinder bore and opened and closed by intake and exhaust valves. A combustion chamber, defined in a cylinder head joined to the upper surface of the cylinder block, permits communication between the intake and exhaust ports and the cylinder bore. A spark plug is mounted in the cylinder head with its electrode facing the combustion chamber.
2. Description of the Prior Art
In such prior art type internal combustion engine, if a swirl of an air-fuel mixture is produced in the cylinder bore, during an intake stroke, the air-fuel ratio of the air-fuel mixture can be uniformized.
Thus, there is a conventionally known side-valve type internal combustion engine in which a side wall of the combustion chamber, adjacent the intake valve, is formed to extend toward an axis of the cylinder bore so as to produce the swirl of the air-fuel fixture within the cylinder bore (see, for example, Japanese Utility Model Publication Laid-open No. 4504/52).
In the prior art engine of the above-described type, however, the flame, i.e., the combustion gas, is not spread over the entire interior of the cylinder bore during an expansion stroke. Such lack of spread results in a non-uniform combustion. Hence, it is difficult to reduce the amount of unburned components in the exhaust gas.